Merge pull request ethereum#12354 from ethereum/addReadBytesFunction

Function to read a number of bytes from an input stream.

libsolutil/CommonIO.cpp

@@ -79,6 +79,17 @@ string solidity::util::readUntilEnd(istream& _stdin)
 	return ss.str();
 }
 
+string solidity::util::readBytes(istream& _input, size_t _length)
+{
+	string output;
+	output.resize(_length);
+	_input.read(output.data(), static_cast<streamsize>(_length));
+	// If read() reads fewer bytes it sets failbit in addition to eofbit.
+	if (_input.fail())
+		output.resize(static_cast<size_t>(_input.gcount()));
+	return output;
+}
+
 #if defined(_WIN32)
 class DisableConsoleBuffering
 {

libsolutil/CommonIO.h

@@ -57,6 +57,10 @@ std::string readFileAsString(boost::filesystem::path const& _file);
 /// Retrieves and returns the whole content of the specified input stream (until EOF).
 std::string readUntilEnd(std::istream& _stdin);
 
+/// Tries to read exactly @a _length bytes from @a _input.
+/// Returns a string containing as much data as has been read.
+std::string readBytes(std::istream& _input, size_t _length);
+
 /// Retrieves and returns a character from standard input (without waiting for EOL).
 int readStandardInputChar();
 

test/libsolutil/CommonIO.cpp

@@ -90,6 +90,15 @@ BOOST_AUTO_TEST_CASE(readUntilEnd_empty)
 	BOOST_TEST(readUntilEnd(inputStream) == "");
 }
 
+BOOST_AUTO_TEST_CASE(readBytes_past_end)
+{
+	istringstream inputStream("abc");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 0), "");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 1), "a");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 20), "bc");
+	BOOST_CHECK_EQUAL(readBytes(inputStream, 20), "");
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 } // namespace solidity::util::test